The present invention is directed generally to paper making machines and, more particularly, to apparatus for guiding a web leader from the press section to the drying section.
Specifically, the present invention is directed to an improvement in apparatus for guiding a web leader, the apparatus being situated after the press section at the initial end of the drying section. The apparatus includes flexible guide members, such as a threading rope, band, or a group of ropes or bands, forming a gap into which the web leader is shifted in the drying section. Various air blow devices guide the web leader towards the drying wire of the drying section, detach the leader from the drying wire and laterally shift the web leader into the gap formed by the threading flexible guide members.
It is conventional in the inital start-up of a paper machine, or in the case where the paper machine is started up after the web has broken, to cut a narrow leader, e.g. having a width of about 200 mm, from the web and then to guide the web leader to threading devices. For example, the web leader can be cut from the web by means of a water jet directed against the web which is situated on a rock roll. The web leader is then usually manually guided to the threading devices by means of air jets. The threading devices in the drying section of a paper machine usually comprise pairs of ropes so that each group of drying cylinders of the drying section is provided with ropes which run over pulleys situated at the ends of the drying cylinders. The leader is usually guided between outer and inner ropes although in some arrangements three jointly operative ropes are used.
As the running speeds of paper machines have increased, an increase in difficulties in threading the end of the web have been experienced. These difficulties are most serious immediately after the press section and at the initial end of the drying section, as well as in the zones between drying cylinder groups.
Conventional threading arrangements require manual guidance of the web leader at several points in the paper machine, including at the drying section. The web leader is manually pulled in a transverse direction in the press section into the gap formed by the threading ropes and it will be understood that such operations involve safety risks due to the close proximity of rotating massive roll components. Additionally, the operator must be experienced in order to insure a reliable threading operation.
An arrangement is disclosed in application Ser. No. 653,825 filed Sept. 24, 1984, now U.S. Pat. No. 4,543,160, assigned to the assignee of the instant application, wherein a narrow leader is cut from a full-width web by means of water jets or the like preferably while the web is situated on a roll in the press section, whereupon the web leader is guided by means of air jets into the gap between the threading ropes from where it is carried between the threading ropes over the drying cylinders.
One feature of the arrangement disclosed in U.S. Pat. No. 4,543,160 is that the leader is detached from the roll in the press section by means of air jets from where the web leader is guided onwardly by means of additional air jets into connection with the drying wire of the drying section. The web leader is detached from the drying wire by means of still additional air jets directed through the drying wire, whereupon transverse air jets are directed at the leader which shift the leader into the gap between the threading ropes and between for subsequent passage through the drying section.
Another feature of the arrangement disclosed in U.S. Pat. No. 4,543,160 is that the air jets which detach the web leader from the drying wire are generated by a blow box or the like situated within the loop of the drying wire in the region of a straight run thereof and proximate to one edge thereof. The blow box is provided with nozzle openings which open toward the drying wire. The means for directing transverse air jets onto the web are situated slightly forwardly of the blow box in the direction of web run. The transverse air jets are directed substantially parallel to the plane of the drying wire at the leader detached from the drying wire by the blow box.
The arrangement disclosed in U.S. Pat. No. 4,543,610 provides a more reliable and faster web threading than was possible prior thereto. It was also possible to automate the web threading operation to avoid or at least reduce the number of risky manual steps involved in the threading of the web.
The arrangement disclosed in U.S. Pat. No. 4,543,160 is also useful in facilitating the threading of the web in the zones between the drying cylinder groups using a closed draw which in turn permits the paper machine to be run at higher speeds and enable the covering angles of the drying wires on the drying cylinders to be increased to thereby enhance the evaporating capacity of the drying section.